[kakwa_]

Also, when architecturing for shards, you must take into account availability.

Having several shards can lower the availability of your application if it cannot handle the absence of a shard.

For example if you have 99.9% availability on your individual DBs, and if you split it up into 10 shards, availability will drop to 99% (8 hours VS 3 days of downtime a year).

To handle that, you need to add replication and automatic fail-overs, adding even more complexity.